How do I add custom membership attributes and display them on the admin page?

The site I am using this plugin on is http://www.fwapl.steadfastclient.com. I have no problem with the functionality of the plugin, everything works fine.

What I would like to know is how I would go about adding custom member attributes to the plugin so that they can be displayed when viewing the "All Members" page on the admin side.

For example, the default attributes shown are username, email, membership level etc. but what if I wanted to add a column labeled "Phone" and how would I get it to display?